1. Technical Field
The disclosure relates to an ink circulation type inkjet printer.
2. Related Art
There is known an ink circulation type inkjet printer which performs printing by ejecting inks from inkjet heads while circulating the inks. The ink circulation type inkjet printer has the following advantages: misfiring of the inks caused by foreign objects in the inks is reduced; and temperature rise in the inkjet heads is suppressed by a cooling effect of the inks achieved by the ink circulation, for example.
The ink circulation type inkjet printer includes an inkjet head and ink tanks disposed upstream and downstream of the inkjet head. These head and tanks are connected to each other by ink conduits. The ink is supplied to the inkjet head from a positive-pressure tank which is the upstream ink tank, and is ejected from the inkjet head. The ink not consumed in the inkjet head is collected by a negative-pressure tank which is the downstream ink tank. The ink stored in the negative-pressure tank is fed to the positive-pressure tank by an ink pump. When the amount of circulating ink decreases, the ink is supplied from an ink cartridge to the negative-pressure tank.
In order for the inkjet head to normally perform ink ejection, a pressure (nozzle pressure) applied to nozzles of the inkjet head needs to be maintained at an appropriate negative pressure. The ink circulation type inkjet printer controls the nozzle pressure by controlling the pressures in the positive-pressure tank and the negative-pressure tank.
An ink circulation type inkjet printer achieving color printing by using inks of multiple colors includes an ink circulation mechanism for each color. Such an inkjet printer needs to be provided with pressure adjustment mechanisms for respective colors so that the pressures of the positive-pressure tanks and the negative-pressure tanks during the ink circulation mechanisms of the respective colors can be controlled color by color. This increases the size of the printer.
In view of this Japanese Unexamined Patent Application Publication No. 2011-167873 proposes a technique in which a common air chamber communicating with the positive-pressure tanks of the respective colors and a common air chamber communicating with the negative-pressure tanks of the respective colors are provided, and the pressures in the positive-pressure tanks of the respective colors and the negative-pressure tanks of the respective colors are controlled through the common air chambers.